The present invention relates to hydraulic circuits and pertains particularly to a hydraulic circuit for a pipelayer to provide all hydraulic functions for the pipelayer.
Pipelayers in the past have typically been constructed with mechanical winches and cables for controlling positioning the boom and hoisting a load. This machine typically has the usual problems associated with the use of cables, clutches and brakes to control the various functions of the machine and its attachments. Cables are quite hazardous and are subject to rapid wear and breakage. The control of the boom and load by means of cable and clutches presents problems of both control and movement of the boom and its load.
The use of hydraulic systems to control and perform these functions has started to come into use recently. However, some of these systems have disadvantages in that they do not provide the necessary precise control and do not have the versatility desired.
The use of hydraulically actuated booms and hoist assemblies is illustrated in U.S. Pat. Nos. 3,265,218 issued Aug. 9, 1966, to Stefanutti; and 3,300,060 issued Jan. 24, 1967, to Lado.